I. Field of the Invention
The present invention relates generally to the field of antenna mounts and more particularly to antenna mounting systems for vehicles wherein the antennas which are utilized present very high wind loads at highway speeds which causes extreme pressure on the antenna mounting system affixed to the vehicle. The antenna system of the present invention typically will lock and secure the antenna to the trunk lid of the vehicle by a unique stabilizing and reinforcing antenna mounting means.
II. Description of the Related Art
Historically, mobile radio operators have been forced by available mechanical support limitations to compromise the radiation efficiency of high wind load antennas typically used in the high frequency bands by mounting them on the periphery of the vehicle. Typical of such peripheral mounting mechanisms would encompass the front and rear bumpers of the vehicle, inasmuch as this is a strong point on most vehicles. However, from a radiation efficiency standpoint, the optimum location on the vehicle for any antenna is always near the horizontal center of mass of the vehicle body.
Mounting antennas on the trunk or hood of the vehicle, these being convenient locations on most vehicles, however, yields nearly the same radiation efficiency of a roof center mounting while providing cost savings and mounting ease opportunities not easily achieved with roof mounting. An important advantage of trunk lip mounting over roof center mounting for many antenna types is the increased radiating element length that is possible when the bottom of the antenna may be placed doser to the ground. This increases the physical length of the antenna without exceeding the normal legal over-the-road height limit, typically at 13'6", for obstruction clearance. For radiation efficiency purposes, the optimum physical length of vertical antennas, which are frequently used in mobile radio service, is 1/4 wave length. Any physical length for a given frequency that is less than 1/4 wave length will be electrically sub-optimal. The practical limit for the physical length of a mobile radio antenna is established only by the actual overhead clearance in the area being traversed by the vehicle. However, as noted above, the legal limit for vehicles operating on public roads is typically 13'6" from the ground to the top of the antenna.
Therefore, it will be obvious that some means of approaching the electrical equivalence of a mobile radio antenna at lower frequencies without exceeding the physical height restriction above the ground is quite desirable. In order to achieve a good radiation efficiency for an antenna, the addition of a relatively large diameter coil, called a loading coil, somewhere along the length of the antenna is required. With the addition of a loading coil, the optimum physical antenna length may now be physically constructed to a shorter form factor. It is this form factor that can produce significant wind load at highway speeds on mobile radio antenna installations, especially those operating below 14 MHz.
Not only will vertically polarized mobile radio antennas benefit by the present invention, but horizontally polarized mobile radio antennas can achieve the same physical and radiation efficiency benefits by the use of the present invention. Horizontally polarized mobile radio antennas typically yield wind loads approaching those of vertically polarized antennas and, in addition, overhead clearance questions may also be a consideration in any stacked array antenna system of any horizontally polarized antenna systems.
The prior art is replete in antenna mounting systems and such systems have been used with antennas of many different configurations. Typical of many vehicle antenna mounting systems are magnetic mounts such as shown in U.S. Pat. No. 4,543,584 to Leer which disclose a horizontally disposed triangular mounting system having magnets at the distal ends of the mount legs for securing to a metal portion of a vehicle. This type of mount, however, will not support a high wind load antenna.
In U.S. Pat. No. 3,967,275 to Wagman and U.S. Pat. No. 4,249,182 to Rupley, clamp-on antenna mounts are shown which are typically clamped to a rearview mirror which is in turn attached to the side of the vehicle cab. While these antenna mounts show a multi-leg attachment system, the mounts are not designed to support high wind load antenna systems.
A typical truck lid mounting system is shown in U.S. Pat. No. 4,028,706 to Dolle, but, again, the system is quite flimsy and will not sustain high wind loading stresses.